Airplane



Dec. 19, 1933. Q NHLBURN 1,940,555

AIRPLANE Filed Nov. 1, 1932 2 Sheets-Sheet 1 INVEN TOR.

Lessher E. Milhum A TTORNEY.

1933- 1.. c. MILBURN 1,940,555

AIRPLANE Filed Nov. 1, 1932 2 Sheets-Sheet 2 I N VEN TOR.

Q Lessiter E. Milhurn QfiJ/W A TTORNE Y.

Patented Dec. 19, 1933 hurrah STATES AIRPLANE Lessiter C. Milburn,Towson, Md, assignor to The Glenn L. Martin Company,- Baltimore,

Application November 1, 1932. Serial No."640,7l

5 Claims. (01. 244-44 My invention relates to multi-engine types ofpropeller driven aircraft.

Airplanes upon which a plurality of propeller units are mounted in aplurality of horizontally 5 spaced geometric planes are longitudinallystable while in flight with a given setting of the horizontal member ofa stabilizer system. The resultant of the several individual thrustsbeing in a given lever arm relation to both the center of gravity of theairplane and the stabilizer system, failure of an auxiliary unit that isconventionally mounted above the main units so changes the turningmoment that the nose of the airplane may be upwardly deflected to suchanextent so as to initiate a stall which may develop into a crash,particularly when the units are forwardly located in relation to thecenter of gravity. The turning moment about the center of gravity caneventually be counteracted by a re-adjustment of the horizontalstabilizer but the available period of time within which to op-- eratethe related mechanism is insufficient to effectively counteract thestalling tendency.

The present invention mounts the propeller units not only in acertainrelation toone another, and to the stabilizer system, but also to thecenters of gravity so that either the failure or elimination of anengine in an upper geometric plane, one which I designate as anauxiliary propeller unit, will not affect the adjusted longitudinalstability of the airplane. The thrust of the auxiliary propeller is sodirected as to produce a downward moment upon the horizontal member ofthe stabilizer system; 35 thus overcoming the normal tendency to noseover while in flight with all engines functioning.

Functional failure of the auxiliary unit results both in a reduction ofthrust and a corresponding reduction of the downward component upon thestabilizer, and therefore neither the longitudinal stability nor thedirection of flight of the craft is altered. Moreover, because thecenter of gravity of the auxiliary unit lies substantially over thecenter of gravity as well as in 5 the plane of symmetry of the airplane,the auxiliary unit can be removed without materially affecting eitherthe center of buoyancy of a seaplane while floating upon water andtaking off, or the inherent stability of the airplane while flying.

The principal object of my invention is therefore to prevent a stallbeing initiated by functional failure of a propeller unit that ismounted above the main power units of an airplane.

Another object is to render it unnecessary to re-adjust the horizontalstabilizer because of 7 reduced thrust while idling an auxiliarypropeller unit.

Another object is to permit removal of an auxiliary propeller unit froman airplane without affecting the inherent longitudinalstability whilein flight. i

Another object is to permit removal of an auxiliary propeller unit froma seaplane without affecting the inherent take-oh character-- istics.

Referring to the drawings".

Fig. 1 is a plan view of a flying boat type of airplane that is equippedwith two main propeller units together with an auxiliary propeller 10unit. r

Fig. 2 is an end elevation of the airplane shown Figure l.

w Fig. 3 is a side elevation of the airplane shown in Figures 1 and 2.515

In the drawings; cargo body 10 is sustained by surface 11 while flying.Tail portion 12 includes a stabilizer system having'a horizontal member13, an elevator 14, and rudders 15l5' under control of the pilot throughconventional mecha- 8O nisms; together with two vertical fins 16-16, allbeing mounted upon tail portion 12. ihe center of" gravity of the craftis indicated at 17 when empty, and at 18 when loaded; and the center ofbuoyancy while floating uponnwater is indicated at 19. Main propellerunits 20--20' are mounted in equilateral relation to the body. The discsof the main propellers are indicated at 21--21, but they may or may notbe located in a common perpendicular plane as shown in 190 the drawings.Auxiliary propeller unit 22 is mounted substantially over the center ofgravity and the center of buoyancy, as well as substantially inequilateral relation to the symmetry of the airplane; the disc of theauxiliary propeller 195 p is indicated at 23, and the center of gravityof the unit is indicated at 24. The geometric plane of the disc isparallel to the-leadingedge of surface 11 as well as angularly relatedto the main propeller discs; angle 30 being such that result ant thrustline 31 of the main propellers intersects thrust line 32 of theauxiliary propeller at a point 33 either upon or above and substantiallyover the horizontal stabilizer and between the vertical fins.v Themaximum stabilizing effect .105 of the auxiliary propeller is attainedwhen the thrust lines intersect the horizontal member of the stabilizersystem.

r The foregoing description of my invention, together with theaccompanying drawings, will tion that when the center of gravity of anauxiliary propeller unit is located substantially over that of theairplane upon which it is mounted substantially in the manner herein setforth together with the aforesaid thrust line relations,

then the longitudinal stability and the take-off characteristics of thecraft are not deleteriously affected whether or not the unit isfunctioning; or the unit can be dismounted without deleteriouslyaffecting either the take-off or flight characteristics of the craftincluding the unit. Conversely; the invention mounts an auxiliary pro-'body; an auxiliary propeller unit mounted above said main units, thecenter of gravity of said unit being located substantially over thecenter of gravity of said aircraft; the plane of the auxiliary propellerdiscforming acute angle with a plane that includes a plurality of mainpropeller discs, and the thrust line of auxiliary propeller intersectinga horizontal member of said stabilizer system. 2. In an aircraft: asustaining surface; a cargo body sustained by said surface,said bodyhaving a tail portion; a stabilizer system connected to said tailportion; a plurality of main propeller units mounted in equilateralrelation to said body, the propellers being ahead of the leading edge ofsaid surface;.an' auxiliary propeller unit mounted within the plane ofsymmetry of said aircraft, the propeller being rearward of the leadingedge'of said surface; the disc of said auxiliary propeller beingangularly related to the discs of said main propellers and the thrustline of said auxiliary propeller intersecting both the resultant thrustline of said main propellers and a horizontal member of said stabilizersystem.

make it clear to those skilled in the art of avia- 3. In an aircraft: asustaining surface; a cargo body sustained by said surface, said bodyhaving a tail portion; a stabilizer system connected to said tailportion; a plurality of main propeller units mounted in equilateralrelation to said body; an auxiliary propeller unit mounted Within theplane ofsymmetry of said aircraft, the propeller being rearward of theleading edge of said surface; the disc of said auxiliary propellerbeingangularly related to the discs of said main propellers; and thethrust line of said auxiliary propeller intersecting both the resultantthrust line of said propellers and a horizontal member of saidstabilizer system.

4. In an aircraft: a sustaining surface; a cargo body sustained by saidsurface, said body having a tail portion; a stabilizer system connectedto said tail portion; a plurality of main propeller units mounted inequilateral relation to said body, the propellers being ahead of theleading edge of said surface; an auxiliary propeller unit mounted withinthe plane of symmetry of said aircraft, the disc of said auxiliarypropeller being angLlarlyv related to the discs of said main propellers;and the thrust line of said auxiliary propeller intersecting both theresultant, thrust line of said main propellers and a horizontal memberof said stabilizer system.

5. In an aircraft: a sustaining surface; a cargo body sustained by saidsurface, said body having a tail portion; a stabilizer system connectedto said tail portion, said system including a plurality of vertical finsmounted upon a horizontal stabilizer; a plurality of main propellerunits, said units being mounted in equilateral relation to said body; anauxiliary propeller unit mounted upon said sustaining surface within thegeometric plane of symmetry, the center of gravity of said unit beingsubstantially over the center of gravity of said body including saidmain units, the disc of the auxiliary propeller being angularly relatedto the discs of the main propellers; and thethrust line of the auxiliarypropellerintersecting the resultant thrust line of the main propellers,the. point of intersection lying between said vertical fins and oversaid horizontal stabilizer.

LESSITER c. MILVBURN.

